There is a known technology in which the content of map data, such as road maps that are used in a navigation apparatus, are partially updated. For example, the apparatus described in Japanese Patent Application Publication No. JP-A-2004-178248 has a structure in which, with respect to a newly constructed road, a data set table is provided that contains a series of link numbers that structure the newly constructed road, in order to maintain the newly constructed road up to points where it links with existing trunk roads as one data set. In addition, in the case where there is an update request for a portion of the segments of the map data, which is partitioned into a plurality of segments, from the navigation apparatus, and in the case where the newly constructed road that is contained in the data set table extends outside the segment for which the update request has been made, the update information for the entire newly constructed road is supplied to the navigation apparatus by referring to the data set table.
Thus, even in the case where update information is supplied for a portion of the segments of the map data that is designated by the navigation apparatus, it is possible to prevent the newly constructed road from being cut off between adjacent segments, and it is possible to ensure that the newly constructed road is connected to the existing trunk road. Therefore, searching for routes that run along the newly constructed road is possible even after the updating of a portion of the segments.
However, inconveniences related to map data that occur due to the updating of a portion of the segments are not limited to those related to newly constructed roads as described above. For example, there may be a case in which an existing road other than a newly constructed road is isolated from other roads. More specifically, as one example, a case will be explained in which, updating of the map data on the map update data supply apparatus side is carried out such that a road (referred to as “road B”) that provides the only connection to a given road (referred to as “road A”) is deleted, and a road (referred to as “road C”) that is connected to the road A is added in a segment that is different from the segment including the deleted road B. In such a case, when the updating of a portion of the segments of the map data on the navigation apparatus side is carried out, if the segment including the deleted road B is assigned as an update target segment and the entire added road C is not included in the update target segment, the road A is isolated and disconnected to any road after updating the map data. In the case where the map data is brought into such a state due to updating, the route search cannot be carried out appropriately when the isolated road is set as the departure point or the destination point, which is a problem.